NEW YORK -LRB- CNN -RRB- -- Diane Sawyer will take over nightly news anchor duties for ABC when Charlie Gibson retires from `` World News '' at the end of this year , a network spokesman confirmed Wednesday .

Charlie Gibson and Diane Sawyer worked together on `` Good Morning America . ''

Sawyer , 63 , will be the second woman to be the solo host of an evening newscast for an American broadcast TV network .

Sawyer will take the chair in January , ABC 's Jeffrey Schneider said .

Gibson , 66 , and Sawyer worked together for years on ABC 's morning show -- `` Good Morning America '' -- before Gibson was promoted over Sawyer to anchor ABC 's `` World News '' in May 2006 .

Elizabeth Vargas and Bob Woodruff co-anchored the newscast before Gibson . That duo came to an end after Woodruff was seriously wounded by a roadside bomb in Iraq .

Maria Brennan , president of the Washington-based American Women in Radio and Television organization , called the announcement a `` watershed moment '' and said Sawyer was the `` obvious choice '' to take over ABC 's anchor chair .

Asked about the significance of two out of three network nightly news anchors being women -- the other being CBS ' Katie Couric -- Brennan said , `` It comes with some excitement and some glee for groups like ours , who have worked for years to ensure that women have parity with their male counterparts . ''

`` When we get to a point in time when we do n't even notice the gender , we can really celebrate , '' Brennan said .

Sawyer worked for President Richard Nixon in the 1970s , first in his White House press office and later helping him write his memoirs after his resignation .

After a stint with CBS News -- including five years as a `` 60 Minutes '' correspondent -- Sawyer joined ABC News in 1989 .

She worked on news magazines for ABC -- including `` Primetime Live '' and `` 20/20 '' -- before being assigned to co-host `` Good Morning America '' with Gibson in 1999 .

CNN 's Albert Lewintinn contributed to this report .

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ABC News anchor Charlie Gibson retiring at end of the year

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Diane Sawyer will take over `` World News '' beginning in January

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The pair worked together for years on `` Good Morning America ''